This invention relates generally to pumping apparatus and more particularly concerns shift valves for submersible downhole pumps.
In my earlier U.S. Pat. No. 4,591,320, issued May 27, 1986 and entitled "Submersible Pumping Unit," a submersible pump provided greatly increased efficiency over previously known submersible pump systems. The improved system uses one of various embodiments of a shift valve assembly to activate a shift rod assembly which in turn transmits reciprocating motion to a piston rod. The piston rod cooperates with a product valve to suck product from the well and push it up the annulus.
While this improved unit of my earlier patent provided greatly improved efficiency over previously known downhole pump systems, the switching time from up-stroke to downstroke of the piston rod approximates twenty to twenty-five milliseconds, allowing the product in the annulus to initiate downward motion between every pump stroke, thus limiting the increased efficiency of the system. This downward flow occurs because an off condition between every positive and negative operation of the shift valve completely interrupts the flow of working fluid driving the piston rod between every stroke of the rod.
If the upward flow of product is maintained relatively constant, this limitation of efficiency resulting from the downward flow of product can be avoided. It is, therefore, a primary object of this invention to provide a shift valve which minimizes the time between up and down strokes of the piston rod. It is a further object of this invention to provide a shift valve which does not have an off condition between positive and negative strokes. Another object of this invention is to provide a shift valve which increases the efficiency of known submersible pumping units.